1. Field of the Invention
The present invention relates to a cylindrical, elongated furnace, preferably a vertical furnace, for treatment of material at high pressures and high temperatures. Furnaces of this kind are used, among other things, for the sintering of metal powder which is contained in a gas-tight capsule and, separated from a pressure gas, is compressed at such a high temperature that the powder is bonded together below the melting temperature; for the treatment of castings, i.e., such that voids are eliminated; and for the joining together of metal pieces. Furnaces for hot isostatic pressing are disclosed in more detail in, for example, U.S. Pat. No. 3,598,378.
2. The Prior Art
In high-pressure furnaces the furnace space must be insulated from the walls of the surrounding pressure chamber since, considering the strength of the material from which the walls are made, these walls must be maintained at a relatively low temperature. In addition, the furnace space must be well insulated with regard to heat losses so as to be able to achieve the desired temperature with a reasonable supply of power. However, the thickness of the insulation must be kept low in view of the fact that the pressure chamber space is expensive and the cost of the pressure chamber rises significantly with increasing diameter. The very high temperatures often used, e.g., normally 1000.degree. C. and more, and the simultaneous high gas pressures, e.g., normally 500 bar and more, involve problems which are very difficult to cope with from the point of view of insulation. The insulation is in fact a very important part of the furnace.
Conventional furnaces normally contain a furnace insulation with a cylindrical mantle having a number of concentric tubes and with layers of insulating material in the gaps between the tubes and, sometimes, outside the outermost tube. In prior art furnaces the inner surface of the innermost tube has always been bare, i.e. uninsulated, because of the difficulties in attaching the insulating material satisfactorily on the side of the furnace space. Particularly in furnaces designed for extremely high temperatures, i.e., 1400.degree. C. and more, the high temperature has involved very difficult problems; particular problems have been caused by deformations due to high temperatures.
It is an object of the present invention to provide a hot isostatic pressure furnace which has even better insulation properties than prior art furnaces of this type.